Spectral analysis of multi mode pulsating sdB stars II. Feige 48, KPD 2109+4401 and PG 1219+534

TL;DR

This study analyzes pulsating sdB stars using high-resolution spectra to determine their atmospheric parameters, metal abundances, and rotational velocities, revealing insights into diffusion processes and stellar composition.

Contribution

It provides detailed spectroscopic analysis of three pulsating sdB stars, highlighting their chemical abundances, low rotation, and diffusion effects, which advances understanding of their atmospheric properties.

Findings

Helium deficiency varies among stars, likely due to diffusion.

Metal abundances are depleted but iron remains solar, confirming diffusion models.

Stars exhibit very low rotational velocities, indicating slow rotation.

Abstract

Three members of the new class of pulsating sdB stars (sdBV or EC 14026 stars) are analysed from Keck HIRES spectra using line blanketed NLTE and LTE model atmospheres. Atmospheric parameters (Teff, log g, He/H), metal abundances and rotational velocities are determined. As is typical for sdB stars, all programme stars are found to be helium deficient, with a He abundance ranging from 1/80 solar for Feige 48 to 1/3 solar for PG 1219+534, probably due to diffusion. Most metals are also depleted. The abundances of C, O, Ne, Mg, Al and Si in the high gravity programme stars KPD 2109+4401 and PG 1219+534 are considerably lower than in the lower gravity stars Feige 48 and PG 1605+072 which could be explained by an equilibrium between gravitational settling and radiative levitation. Surprisingly iron is solar to within error limits in all programme stars irrespective of their gravity, confirming predictions from diffusion calculations. The metal lines are very sharp and allow the microturbulent velocity to be constrained to be lower than 5km/s (KPD2109+4401, PG 1219+534). Also the projected rotational velocities have to be very low (vrot sini<10km/s). For Feige 48 the limits are even tighter (vmicro<=3km/s, vrot sini<=5km/s).